This invention generally relates to electrical switch construction and more particularly to push-button electrical switch construction of the type having a spring-loaded actuator for momentary-on electrical contact and for stable-on electrical contact.
In the field of electrical switch construction, push-button switches that provide connections between a first terminal located on the push-button and a second terminal in the body of the switch are extremely useful for a number of applications. Such switches are employed in a number of electrical and electronic applications which may include electrical appliances, hand-held electrically operated devices and a plurality of automotive electrical applications for both direct and alternating current.
One conventional method of constructing such push-button switches consists of mounting a miniature switch mechanism beneath a push-button. The push-button operates a ratchet or other mechanical device that moves the single-throw miniature switch to different positions upon repeated actuation of the push-button. While such an assembly is useful for many purposes and provides a relatively simple and robust construction, the life expectancy or longevity of such a switch is limited. Such push-button switches are not designed for repetitive operation such that the components of the switch tended to wear rapidly.
Push-button switches of the past employed a cantilever type spring for making electrical contact between the spring-loaded switching mechanism and a fixed terminal in electrical communication with an electrical conductor. Once the push-button switch was activated, a pathway was created for the transfer of electrical load through the fixed terminal of the switch.
A cantilever spring is a straight member mechanically attached at only one end. The attached end is normally connected to the fixed terminal in the bottom cover portion while the shaft of the cantilever spring includes sufficient flexibility to connect and disconnect the electrical circuit upon contacting a conductive element operated by the push-button actuator. A particular example of one such push-button switching device employs a biasing spring and a compound cantilever spring. The cantilever spring must be accurately positioned within the bottom cover portion to maintain the proper switching tolerances with respect to a movable metallic cup contact. The push-button switching device utilizes a vertical spline design. Thus, once the push-button and biasing spring are depressed beyond the point of ratchet, the metallic cup contact is rotated to the first "on-position" in contact with the cantilever spring.
During the next operation of the push-button, the cup contact is rotated again separating it from the cantilever spring for achieving the second "on-position". In the second "on-position", the biasing spring is relaxed permitting the ratchet mechanism to travel to the top of the recesses located between the vertical splines. In this position, the cup contact completes electrical communication with a stationary contact for energizing a second circuit. Thus, in this example, the switch completes an electrical circuit in both positions. Further, partial deflection of the push-button which is insufficient to exceed the point of ratchet results in momentary contact between the cup contact and the cantilever spring.
After a plurality of operations, the cantilever spring tends to adopt a permanent set position with respect to the actuator terminal because of a loss of resiliency. The loss of resiliency is due to the short active length of the cantilever spring resulting in less stability with a higher probability of deformation to a permanent set position. Further, the cantilever spring has a tendency to yield which causes the cantilever spring to shorten and to lose contact with the actuator terminal of the push-button switch. This causes the push-button switch to loose its effectiveness as a switching device.
Another example employs a push-button switch for electronic equipment having reduced size, improved reliability and stabilized contact resistance by employing a coil spring having a large diameter base section with a reduced diameter top section. The improvements are achieved by bending that part of the coil spring having the reduced diameter into the spring to face the side of the larger diameter base. The inner surface of the push-button is shaped like a truncated cone whose lateral surface is a guide for the coil spring mounted in the push-button.
When the push-button is depressed, the coil spring is compressed so that the reduced diameter section of the coil spring touches a pair of contacts to complete the electrical circuit between the contacts via the spring. After complete depression, the push-button is seated with its conical surface on the lateral surface of the coil spring. Contact pressure is acquired by having the reduced diameter section of the coil spring facing in the direction of the larger diameter section. This push-button switch provides only momentary contact.
A third example teaches a switch of the tumbler type which employs a mercury button for electrical contacts. Rotation of a finger member over a limited arc is effective to open or close an electric circuit according to the direction in which the finger piece is rotated. A lamp or other indicating means is employed to operate either as a "pilot" or a "beacon" according to whether the lamp is connected in series or parallel with the switch conductors. This switch does not utilize a ratchet indexing device.
Another example includes a small versatile electrical switch suitable for the control of low current electrical devices employing a biasing spring, a ratchet indexing device, and a pair of symmetrically spaced terminals for completing an electrical circuit. Two final examples each include a pair of coil springs with the first switch comprising a push-button which is movable in a casing and enclosed by a boot made of flexible material. The first switch includes linkage for rotating the switch during successive switching operations. The second switch comprises an alternate action push-button switch which converts longitudinal motion of the push-button to alternate circumferential rotation of a rotating means. The rotating means alternately opens and closes a contact.
Hence, those concerned with the development and use of push-button switching devices in the electrical field have long recognized the need for improved push-button switches which extend the longevity of the switch by improving the resiliency of the actuator terminal and which eliminates permanent deformation and yielding of the spring for improved operation. The present invention fulfils all of these needs.